1. Field of the Invention
The present invention relates to a semiconductor device having a semiconductor chip, and a process for producing the same, and in particular to a semiconductor device having a structure wherein a groove or holes are made in a substrate on which bumps for electrical connection from its back surface are formed, i.e., a substrate for bumps, and/or in an adhesive for bonding the substrate for the bumps to a semiconductor chip, and a process for producing the same.
2. Description of the Related Art
Recently, the number of external terminals in semiconductor devices has increased with an increase in the integration degree thereof. In some cases of semiconductor devices having such a high integration degree, a semiconductor chip is not directly mounted on a substrate but is mounted on a substrate through a substrate for bumps, such as a tape on which solder bumps are formed. FIG. 1A is a plan view illustrating a structure of a semiconductor device in a prior art, and FIG. 1B is a cross section taken on F--F line of FIG. 1A.
As shown in FIGS. 1A and 1B, a semiconductor chip 700 is connected to a tape 400 as a substrate for bumps with an adhesive 600. Electrodes 300a are formed at the external terminal side of the tape 400, and electrodes 300b are formed at the side of the semiconductor chip 700 thereof. Each of the electrodes 300a is connected to each of the electrodes 300b through a wiring circuit arranged inside the tape 400.
Electrodes 300c are formed at the tape 400 side of the semiconductor chip 700. The electrodes 300b are connected to the electrodes 300c through bumps 500. An adhesive agent 600 is injected into the region between the semiconductor chip 700 and the tape 400 after the connection of the electrodes through the bumps 500. Solder balls 200 are formed on the electrodes 300a of the tape 400. This semiconductor device is mounted on a substrate (not shown) through the solder balls 200.
In the semiconductor device having the above-mentioned structure, the area where the solder balls are mounted becomes large if the number of the solder bumps, which are external terminals, increases. Therefore, if the semiconductor device is mounted on the substrate and subsequently stress is generated by a change in temperature, there arises a problem that the solder balls 200 subjected to the stress are broken so as to become open inferiority.
Such stress is generated by the difference in the thermal expansion coefficients between the semiconductor device and the substrate on which the semiconductor device is mounted. When the change in temperature is generated by the operation of the semiconductor device so that its temperature rises, the semiconductor device and the substrate expand. When the temperature falls, the semiconductor and the substrate contract. In these cases, if the thermal expansion coefficients of the substrate and the semiconductor device are different from each other, the degrees of the expansion and contraction are different. In general, the substrate expands and contracts more greatly than the semiconductor device. When such expansion and contraction are repeated many times, stress is structurally concentrated mainly in joint portions of the solder balls 200. For this reason, the solder balls 200 are broken to become open inferiority.
A semiconductor device for overcoming such drawbacks is proposed (Japanese Patent Application Laid-Open No. Hei 8-55875, published on Feb. 27, 1996). FIG. 2 is a cross section illustrating a structure of a semiconductor device, in the prior art, disclosed in the Japanese Patent Application Laid-Open No. Hei 8-55875. FIG. 3 is a plan view illustrating a mounting structure of a semiconductor chip and a package substrate in the semiconductor device illustrated in FIG. 2.
In the semiconductor device disclosed in this publication, a package substrate 410, which is a substrate for bumps and on which a semiconductor chip 710 is mounted, is divided into 4 pieces. The semiconductor chip 710 is mounted on a module substrate 800 through the package substrates 410. The whole of the semiconductor chip 710, including bump electrodes 510, is packaged and fixed by means of a molding resin 610. The four package substrates 410 and the module substrate 800 are connected to each other through bump electrodes 210.
According to the semiconductor device in the prior art, disclosed in the above-mentioned publication, the package substrate, on which the semiconductor chip 710 is mounted is divided into the 4 package substrates 410; therefore, the maximum distance L1 between the bumps is not more than 1/2of the maximum distance L0 between the bumps in the case that the package substrate is not divided, as illustrated in FIG. 3. This results in reduction in strain which is applied to the bump electrodes 510 by a change in temperature.
However, even if the package substrate is composed of the 4 divided package substrates 410, regions between the package substrates 410 are embedded by the molding resin 610. Accordingly, these are substantially integrated with each other. For this reason, the stress based in the change in temperature is transmitted through the molding resin 610 by which the regions between the 4 package substrates 410 are embedded, so that the strain applied to the bump electrodes 510 is not sufficiently reduced.
According to the above-mentioned publication, no consideration is given to the reduction in the stress based on the temperature-change between the package substrates 410 and the module substrate 800.
In order to mount the semiconductor chip 710 on the 4 package substrates 410 resulting from the division, the following steps are necessary: the step of positioning the 4 package substrates 410 to each other at a given interval, the step of mounting the semiconductor device 710 under the condition that the distance between the respective package substrates 410 is kept and fixed, and the step of packaging the semiconductor device 710 by means of the molding resin 610. However, it is very difficult to position the divided package substrates to each other. Moreover, there remains a problem that the mounting requires much time since the number of the steps increases.